Stringline attachment for paving machine



Sept. 13, 1966 F. M. BRAKE:

STRINGLINE ATTACHMENT FOR PAVING MACHINE Filed Jan. 5l, 1965 INVENTOR fzA?. fe/ 8%@ M NN N N\\\ \N k www, T \f O M o www www x N. .NW \N\ M wATTORNEYS United States Patent O 3,272,099 STGMNE ATTACHMENT FR PAVINGMACHINE Frank M. Drake, Topeka, Kans. (612 W. 47th St., Kansas City, Mo.64112) Filed dan. 31, 1963, Ser. No. 255,332 9 Claims. (Cl. 94-46) Thisinvention relates to paving machines, and in particular to machines forresurfacing existing roads, In such use, the `worn road presents surfaceirregularities which would persist in the resurfaced road unlesscompensated for. Commonly, this problem is dealt with by appropriatemanipulation of a levelling screed, in association with a sensing meansfor detecting irregularities in the road surface.

In its generalized form, such a screed is towed along behind the mainbody of the paving machine, at the rear ends of a pair of relativelylong arms, swingably mounted by means of trunnions on the pavingmachine. With this arrangement, the lower, trowelling surface of thescreed may assume an angle of attack in riding over the iuid pavingmaterial, and for a given arm, as to arrangement and effective length,and attitude of the screed with respect to the arm, as well as physicalcharacter of the material being spread, there is a critical value of theangle of attack, which persists fas long as the paving machine treads orwheels are pursuing a level, forward path. However, when ir-regularitiesare encountered, compensation is made, and to this end, the screed isarranged for pivotal motion, to vary the angle of attack, suchadjustment being usually provided for by means of a screw and handwheelat each end of the screed. Usually a sensing means is provided, todetect irregularities of the pavement in advance of the screed, and thescreed adjusted accordingly. The sensing means may partake of variousforms, with signals being detected visually or electrically, Ior byother means, and the screed is either adjusted manually, or auto*rnatically through suitable servo-mechanisms. Thus, basically, thesensors detected swing in the screed arms as the paving machine departedfrom a normal, level line, but in later, improved modifications, theattitude of the screed in relation to t-he main body of the machine hasbeen magnified by a lever system super-imposed on the screed arms andproviding a magnified swing of a socalled projected point of the screedsurface, for pickup by the sensor. Although the latter system will beemployed in illustrating the workings of the present invention, it willbe understood that the invention may also be practiced in associationwith any acceptable sensing means.

In conventional, re-paving practice, it is customary to lay a stringlinealong and to one side of the center of a roadway, supported on stakes atabout 25 foot intervals, and defining the proposed level of the newpaving surface. In the initial pass of tamping and spreading thesurfacing material, the screed attitude is varied, as required by thesensor, to compensate for indicated departures of the sensor from thestringline. Control of surfaces on subsequent passes utilizes what isknown as a fiat line, wherein the stringline is placed flat on thepreviously laid surface, .and spans any irregularity that might remainfrom the initial spreading operation. Thus, there is a gradual andcontinuing improvement for each pass, but the laying of a stringline bya crew of men, for each pass, is entailed. The lat line is effective ifthe initial pass has been properly accomplished; or in other words, ifirregularities have been reduced in length to less than fifty feet.

It is a general object of the invention to improve the sensingmechanism, looking to more elicient reduction of irregularities duringany -given pass. Another object is to avoid the need for staking outstring-lines. More particularly, it is an object to provide a stringlinefor sensing 3,272,099 Patented Sept. 13, 1966 ICC which forms a part ofthe paving machine, and is carried along therewith. A still furtherobject of the invention to substantially increase the effective lengthof the main body of the machine, so that irregularities of great lengthmay be made manifest by attitudes of mechanism forming part ofthemachine.

These and objects, which will be apparent, are attained by the presentinvention, a preferred form of which is described in the followingspecification, as illustrated in the drawing, in which:

FIGURE l is a side elevational view of a paving machine, on `which ismounted a travelling stringline, according to the invention; and

FIGURE 2 is a top plan View of the apparatus shown in FIGURE 1.

Referring to the drawing by characters of reference, there is shown apaving machine, the body of which is indicated generally by the numeral10. The machine is supported on suitable endless track systems 12, andcarries a hopper 14, for dispensing the paving mix in advance of thescreed 18. A bumper roller 16 on the forward edge of the hopper 14,limits the backing movement of dump trucks used in filling the hopper.

In its smoothing operation, the screed 18 oats on the surfacingmaterial, and to this end, is carried by a pair of rocker arms 20, 22,located on opposite sides of machine 10, and independently swingable ona common, horizontal axis, by virtue of pivotal mounting of theirforward ends on :trunnions 24, carried by brackets 26, depending frommachine 10. The two ends of the screed 1S are attached to the respectiverocker arms 20, 22 by pivot pins 28, so that the angular disposition ofthe bottom, or trowelling surface 30, of a screed end with respect toits `associated rocker arm may be varied. In order to make thisadjustment, the screed-rocker arm system is provided, at each end, withIan adjusting screw 32, which is anchored for free rota-tion in a block34, carried rearwardly of the screed and is threaded in a block 36,carried at the rear end of the associated rocker arm. Although thescreed, rocker arm, and screw present a fixed quadrilateral duringoperation, there is a skewing act-ion during screw adjustment, and forthis reason, block 34 is mounted on a pivot 38, and block 36 on a pivot40. Screws 32 are turned by double cranks 42, and it will be seen thatscrew action tending to move block 36 toward block 34 will lower theangle of attack of the screed in its Afree drag by the rocker arms.

The critical angle of the screed determines a constant thicknes-s oflaid material, assuming an even bed. However, when irregularities areencounted, these are followed by the main body of the machine, whichcauses a relative swing of the rocker arms, and hence the effectiveangle of the screed, which would result in too thin or too thick a layerunless adjustments were made. The end result sought is to have the pathof progress of the screed at or parallel to the istringline, and to thisend, departures of a reference point on the machine with respect to thestringline are picked up by fthe sensor, and the screed appropriatelyadjusted so as to continue to move parallel to the stringline.

In the illustrated embodiment, the sensing means is mounted on aleverage system which magnies angular changes of the screed by locatingthe sensor at a point projected forwardly of the screed. Thisarrangement, which is conventional, is shown as comprising a pair oflong lever arms '43, rockable on a pair of knifeedge supports 44, joinedat their forward ends by a cross bar 46, and the rear end of eachconnected to the tail end of screed 1S through la turnbuckle link 43.The sensing means, which may consist of any of several conventionaltypes, and which is therefore shown only very generally, is carried byan arm 50, carrying a laterally extending arm 52, from which a furtherarm 54 extends rearwardly, the latter carrying a cradle 56, in which atrolley-type sensor having a shaft 58, and roller 60, are mounted. Itwill be understood that the sensor 58-60, whatever its specific type,will have a sensitivity to contact with a stringline, of the order ofthat found in sensitive micro switches, so as to be capable ofengendering a signal upon the slightest departure from contact. Thereis, thus, little or no load on the stringline.

The present invention contemplates a stringline, in association withconventional paving mechanism, of which the foregoing describedstructure is a typical, and preferred example. That is to say, whereasthe sensor contact 60 would ordinarily cooperate with a stake-supportedstringline, the present invention contemplates its coaction with astring carried by, and therefore travelling with, the paving machine.Thus, one side of the machine carries a stub shaft 62, on which isjournaled the central sleeve 64 of a walking beam comprising a rear arm66 and a front `arm 68. The arms are of considerable length, and inorder to -provide against bending they are constructed along the linesof a dihedral angle in cross-secition, and are of open-workconstruction, to keep weight to a minimum. Thus, each has a central,llongitudinal rail, or backbone 70, and two, outer, longitudinal rails72, the inner rail being joined to the outer rails by chevron struts, orherringbone ribs 74. Further transverse struts may be provided on theunder side of arms 66, 68, if deemed necessary or desirable. However,since these arms are intended only to carry a stringline, the loaddemands -are very slight. Each arm carries, at its outer end, a groundroller 76, which may be of the caster type. Adjacent the rollers, eacharm has an angularly disposed bracket 78, and to these brackets the twoends of the travelling .stringline 80 are attached. Although not shown,it will be understood that proper tensioning means for the stringlinewill be provided, either built-in, or as a separate tool. In lieu of thewire or cord 80, alight ray running between the wheels 76 may be used asa reference line, and in this case a photocell may be used as a sensor.In the case of a string or wire, it is also possible to use two rockerarms, mounted on two separate shafts, and in this case the line will beautomatically tensioned at all times.

The |use of the travelling stringline is tantamount to using a pavingmachine having an extremely long wheel base for picking up roadirregularities. The sensor is located about midway between thesupporting wheels 76, and therefore averages out the vertical spread inany given irregularity. The results dier from those of the at line,mentioned above, in that in the case of the at line the paver fills upthe low places and builds up to the high places, whereas in the case ofthe travelling stringline the paver lls up approximately half of the lowplaces and builds up to only half of the high places. The travellingline produces a profile which, while not free of irregularities, isnevertheless considerably smoothed in comparison to the profile overwhich it travels. As a result, the surface obtained on the third and-fourth passes is quite smooth, particularly if the surface beingrecovered has only relatively short sags and humps.

The effectiveness or smoothing ability of the travelling stringlinedepends on the relation of the distance between the support wheelstherefor and the lengths of the existing irregularities. When theoverall length of an irregularity is greater than twice the distancebetween the support wheels, the ends of the irregularities becomeindividual irregularities, and the overall irregularity is onlydecreased. While the travelling stringline minimizes all irregularities,it eliminates shorter ones.

The travelling stringline effects a great saving in manpower, since itrequires no setting and resetting of a stationary stringline. Thisinherent principle, with contherefore, be deemed as limited, exceptinsofar as shall appear from the spirit and scope of the appendedclaims.

I claim:

1. In a paving machine of the type having a main body, mobile on aroadway, a screed carried in towed relation on a pair of rocker armspivoted on said body, means adjustably connecting said screed and saidarms to vary the attitude of said screed with respect to said rockerarms, means operatively associated with said screed magnifying changesin attitude of said screed and sensing means carried by said magnifyingmeans, the improvement comprising rst means pivotally supported by themachine and travelling on the roadway well in advance thereof, secondmeans pivotally supported on the machine and travelling on the roadwayto the rear of the machine and third means connecting points on the rsttwo means adjacent their respective contacts with the roadway, in astragiht line, said sensing means being located to respond to a pointmidway of said third means, whereby the attitude of the screed is maderesponsive to the average of changes in level of the roadway at thecontact points.

2. A machine as in claim 1 wherein said rst and second means are armscomprising a walking beam pivotally supported by the machine havingroadway contacts at the ends of the beam arms and the third means is astringline extending between points adjacent the roadway contacts.

3. A machine as in claim 1 wherein the roadway contacting elements arecaster wheels.

4. In a paving machine of the type having a main body, mobile on aroadway, a screed carried in towed relation on a pair of rocker armspivoted on said body, means adjustably connecting said screed and saidarms to vary the attitude of said screed with respect to said rockerarms, and sensing means operatively associated with said screed, theimprovement comprising an elongated walking beam medially pivoted to andextending well in advance of and to the rear of said body, on a shaftextending laterally from one side thereof, a ground-engaging wheelcarried at each of the outer ends of said walking beam, anchor means fora stringline carried by said walking beam near each end thereof, and astringline attached at its ends to said anchor means said sensing meansbeing 1n contact with a point midway of said stringline.

5. In a paving machine of the type having a main body, mobile on aroadway, a screed carried in towed relation on a pair of rocker armspivoted on said body, means adjustably connecting said screed and saidarms to vary the attitude of said screed with respect to said rockerarms, and sensing means operatively associated with said screed, theimprovement comprising an elongated walking -beam medially pivoted toand extending well in advance of and to the rear of said body, on ashaft extending laterally from one side thereof, a groundengaging membercarried at each of the ends of said walking beam, and a stringline, saidstringline being anchored to said walking beam near each end thereofsaid sensing means being in contact with a point midway of saidstringline.

6. In a paving machine of the type having a main body, mobile on aroadway, a screed carried in towed relation on a pair of rocker armspivoted on said body, means adjustably connecting said screed and saidarms to vary the attitude of said screed with respect to said rockerarms, and sensing means operatively associated with said screed, theimprovement comprising an elongated walking beam medially pivoted to andextending well in advance of and to the rear of said body, on a shaftextending laterally from one side thereof, and a ground-engaging wheelcarried at each of the outer ends of said walking beam, a stringline,said walking beam carrying said stringline between said wheels saidsensing means being in contact with a point midway of said stringline.

7. In a paving machine of the type having a main body, mobile on aroadway, and a screed mounted for swinging movement, 4as a whole, abouta transverse axis on said body, and adapted Ifor adjustment of attitudeapart from its axis of swing, by sensor means responsive to yan elementresponding to a condition of the roadway, the improvement comprising apair of arms extending, respectively, forwardly and rearwardly of saidbody, at one side thereof, and adapted for swinging movement on a pivot,mounted on the main body, in a vertical plane, a ground-engaging membercarried at the end of each arm, and a reference guide line extendingfrom an outer portion of one of said arms to an outer portion of theother of said arms a point on the reference guideline being the elementused as the basis for `adjusting the attitude of the screed.

8. A machine as in claim 7, said wheels being of the caster type.

9. A `machine as in claim 7, said arms being mounted on separate axes.

7/1930 Lamb. 7/1934 Pierce.

FOREIGN PATENTS Germany.

References Cited by the Applicant UNITED STATES PATENTS Gardiner.

Barber.

Baker.

Johnson.

Heer.

Bowen.

Shea.

Watters.

CHARLES E. OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, Examiner.

N. C. BYERS, Assistant Examiner.

4. IN A PAVING MACHINE OF THE TYPE HAVING A MAIN BODY, MOBILE ON AROADWAY, A SCREED CARRIED IN TOWED RELATION ON A PAIR OF ROCKER ARMSPIVOTED ON SAID BODY, MEANS ADJUSTABLY CONNECTING SAID SCREED AND SAIDARMS TO VARY THE ATTITUDE OF SAID SCREED WITH RESPECT TO SAID ROCKERARMS, AND SENSING MEANS OPERATIVELY ASSOCIATED WITH SAID SCREED, THEIMPROVEMENT COMPRISING AN ELONGATED WALKING BEAM MEDIALLY PIVOTED TO ANDEXTENDING WELL IN ADVANCE OF AND TO THE REAR OF SAID BODY, ON A SHAFTEXTENDING LATERALLY FROM ONE SIDE THEREOF, A GROUND-ENGAGING WHEELCARRIED AT EACH OF THE OUTER ENDS OF SAID WALKING BEAM, ANCHOR MEANS FORA STRINGLINE CARRIED BY SAID WALKING BEAM NEAR EACH END THEREOF, AND ASTRINGLINE ATTACHED AT ITS ENDS TO SAID ANCHOR MEANS SAID SENSING MEANSBEING IN CONTACT WITH A POINT MIDWAY OF SAID STRINGLINE.